As is well known, arylamines have been made in a variety of ways including reduction of the corresponding nitro compound, reaction of a chloro compound with ammonia either along or with catalysts such as copper salts, reaction of phenols with ammonia and zinc chloride at an elevated temperature and by the well-known Hofmann amide rearrangement with a hypohalite or halogen and a base. For some time, more direct methods of producing arylamines have been sought.
More recently, Canadian Pat. No. 553,988 issued on Mar. 4, 1958, to Thomas describes a one-step process for the production of aromatic amines. One embodiment comprises contacting a mixture of benzene, ammonia and oxygen in the vapor phase with a platinum catalyst maintained at a temperature of about 1000.degree.C. In another embodiment, a mixture of benzene and ammonia is contacted in the vapor phase with a reducible metal oxide such as nickel oxide at a temperature of about 100.degree.C. to 1000.degree.C. The benzene is directly converted to aniline as represented by the equation EQU C.sub.6 H.sub.6 + NH.sub.3 + MO .fwdarw.C.sub.6 H.sub.5 NH.sub.2 + H.sub.2 O + M,
wherein M represents the metal and MO represents the oxide thereof.
U.S. Pat. No. 2,948,755 issued on Aug. 9, 1960 to Louis Schmerling describes the preparation of aromatic amines by reacting an aromatic compound such as benzene with anhydrous ammonia in the presence of a compound of a group VI-B metal such as molybdenum, tungsten or chromium and a promoter consisting of an easily reducible metallic oxide such as an oxide of copper, iron, nickel, silver or gold at a temperature in the range from about 200.degree. to 600.degree.C. The easily reducible metallic oxide is stated to perform as a hydrogen acceptor to thus remove the by-product hydrogen produced, causing the reaction to proceed in the desired direction.
An earlier reference, J. B. Wibaut, Berichte, 50, 541-6 (1917), reported the synthesis of aniline by passing benzene and ammonia through an iron tube packed with reduced nickel, iron and asbestos at a temperature in the range of 550.degree. to 600.degree.C.
While the methods of these references do provide direct processes for the production of aromatic amines, they do so in low conversions and yields of the aromatic compound to aromatic amines.
In an attempt to obviate these problems, it has been proposed to carry out the reaction between ammonia and the aromatic compound in the presence of a conditioned nickel/nickel oxide/zirconium oxide cataloreactant, so named because it acts as a catalyst as well as a reactant in the direct amination of an aromatic compound with ammonia. Prior to use in the reaction the cataloreactant is conditioned. That is, the nickel oxide component of the cataloreactant is partically reduced to elemental nickel in a reducing atmosphere such as hydrogen. The elemental nickel formed by this process is partially oxidized back to nickel oxide in an oxidizing atmosphere such as oxygen, air or water. In spite of the improved results achieved using such catalysts, the demands of production make it necessary to continue the search for still better catalysts which yield still higher conversions.